Form Complexes (form + complex)

Distribution by Scientific Domains


Selected Abstracts


Transmitting the signal of excess nitrogen in Saccharomyces cerevisiae from the Tor proteins to the GATA factors: connecting the dots

FEMS MICROBIOLOGY REVIEWS, Issue 3 2002
Terrance G. Cooper
Abstract Major advances have recently occurred in our understanding of GATA factor-mediated, nitrogen catabolite repression (NCR)-sensitive gene expression in Saccharomyces cerevisiae. Under nitrogen-rich conditions, the GATA family transcriptional activators, Gln3 and Gat1, form complexes with Ure2, and are localized to the cytoplasm, which decreases NCR-sensitive expression. Under nitrogen-limiting conditions, Gln3 and Gat1 are dephosphorylated, move from the cytoplasm to the nucleus, in wild-type but not rna1 and srp1 mutants, and increase expression of NCR-sensitive genes. ,Induction' of NCR-sensitive gene expression and dephosphorylation of Gln3 (and Ure2 in some laboratories) when cells are treated with rapamycin implicates the Tor1/2 signal transduction pathway in this regulation. Mks1 is posited to be a negative regulator of Ure2, positive regulator of retrograde gene expression and to be itself negatively regulated by Tap42. In addition to Tap42, phosphatases Sit4 and Pph3 are also argued by some to participate in the regulatory pathway. Although a treasure trove of information has recently become available, much remains unknown (and sometimes controversial) with respect to the precise biochemical functions and regulatory pathway connections of Tap42, Sit4, Pph3, Mks1 and Ure2, and how precisely Gln3 and Gat1 are prevented from entering the nucleus. The purpose of this review is to provide background information needed by students and investigators outside of the field to follow and evaluate the rapidly evolving literature in this exciting field. [source]


Two major Smad pathways in TGF-, superfamily signalling

GENES TO CELLS, Issue 12 2002
Keiji Miyazawa
Members of the transforming growth factor-, (TGF-,) superfamily bind to two different serine/threonine kinase receptors, i.e. type I and type II receptors. Upon ligand binding, type I receptors specifically activate intracellular Smad proteins. R-Smads are direct substrates of type I receptors; Smads 2 and 3 are specifically activated by activin/nodal and TGF-, type I receptors, whereas Smads 1, 5 and 8 are activated by BMP type I receptors. Nearly 30 proteins have been identified as members of the TGF-, superfamily in mammals, and can be classified based on whether they activate activin/TGF-,-specific R-Smads (AR-Smads) or BMP-specific R-Smads (BR-Smads). R-Smads form complexes with Co-Smads and translocate into the nucleus, where they regulate the transcription of target genes. AR-Smads bind to various proteins, including transcription factors and transcriptional co-activators or co-repressors, whereas BR-Smads interact with other proteins less efficiently than AR-Smads. Id proteins are induced by BR-Smads, and play important roles in exhibiting some biological effects of BMPs. Understanding the mechanisms of TGF-, superfamily signalling is thus important for the development of new ways to treat various clinical diseases in which TGF-, superfamily signalling is involved. [source]


Comparative Study of Activities between Verbascoside and Rutin by Docking Method

MOLECULAR INFORMATICS, Issue 1 2003
Kun Gao
Abstract Verbascoside and rutin possess anti-cancer properties and are capable of repairing DNA damaged by oxygen radicals, acting as powerful antioxidants. Based on kinetic measurements and experiments on tumor cells, docking studies of the two ligand molecules with the receptor telomeric DNA fragments have been carried out. The docking calculations performed using JUMNA software showed that the both molecules can be docked into the minor groove of telomeric DNA and form complexes with suitable geometry for electron transfer between guanine radical and ligands. The reaction mechanism via the electron transfer process is further confirmed through energy calculations for transition states using MOPAC 93 program. Complexes can be formed without major distortion of DNA structure and are further stabilized by the interaction of DNA with the saccharide side-groups. By comparing their energies, the difference of activities of the two compounds can be explained. [source]


Metal-ion dependence of the active-site conformation of the translesion DNA polymerase Dpo4 from Sulfolobus solfataricus

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 9 2010
Adriana Irimia
Crystal structures of a binary Mg2+ -form Dpo4,DNA complex with 1,N2 -etheno-dG in the template strand as well as of ternary Mg2+ -form Dpo4,DNA,dCTP/dGTP complexes with 8-oxoG in the template strand have been determined. Comparison of their conformations and active-site geometries with those of the corresponding Ca2+ -form complexes revealed that the DNA and polymerase undergo subtle changes as a result of the catalytically more active Mg2+ occupying both the A and B sites. [source]


Computational Design of Four-Helix Bundle Proteins That Bind Nonbiological Cofactors

BIOTECHNOLOGY PROGRESS, Issue 1 2008
Andreas Lehmann
Recent work is discussed concerning the computational design of four-helix bundle proteins that form complexes with nonbiological cofactors. Given that often there are no suitable natural proteins to provide starting points in the creation of such nonbiological systems, computational design is well suited for the design and study of new protein-cofactor complexes. Recent design efforts are presented in the context of prior work on the de novo design and engineering of porphyrin-binding four-helix bundle proteins and current developments in nonlinear optical materials. Such protein-nonbiological cofactor complexes stand to enable new applications in protein science and materials research. [source]


CDK2 regulation through PI3K and CDK4 is necessary for cell cycle progression of primary rat hepatocytes

CELL PROLIFERATION, Issue 4 2007
L. Wierød
In response to mitogenic stimuli, CDK4 and CDK2 form complexes with cyclins D and E, respectively, and translocate to the nucleus in the late G1 phase. It is an on-going discussion whether mammalian cells need both CDK4 and CDK2 kinase activities for induction of S phase. Methods and results: In this study, we have explored the role of CDK4 activity during G1 progression of primary rat hepatocytes. We found that CDK4 activity was restricted by either inhibiting growth factor induced cyclin D1-induction with the PI3K inhibitor LY294002, or by transient transfection with a dominant negative CDK4 mutant. In both cases, we observed reduced CDK2 nuclear translocation and reduced CDK2-Thr160 phosphorylation. Furthermore, reduced pRb hyperphosphorylation and reduced cellular proliferation were observed. Ectopic expression of cyclin D1 alone was not sufficient to induce CDK4 nuclear translocation, CDK2 activity or cell proliferation. Conclusions: Thus, epidermal growth factor-induced CDK4 activity was necessary for CDK2 activation and for hepatocyte proliferation. These results also suggest that, in addition to regulating cyclin D1 expression, PI3K is involved in regulation of nuclear shuttling of cyclin-CDK complexes in G1 phase. [source]


Dynamic Molecular Tweezers Composed of Dibenzocyclooctatetraene Units: Synthesis, Properties, and Thermochromism in Host,Guest Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2009
Tomohiko Nishiuchi
Abstract Novel dynamic molecular tweezers (DMTs) 3,a, 3,b, 4,a, 4,b, and 5,b, composed of two tub-shaped dibenzocyclooctatetraene (DBCOT) units, were designed and synthesized. The cyclooctatetraene (COT) rings of these DMTs readily invert in solution, and the molecular structure shows rigid syn and anti forms in an equilibrium mixture in solution. The syn and anti conformers can be observed by NMR. The isomerization barriers of 3,a, 3,b, 4,a, 4,b, and 5,b are in the range of 16.5,21.3,kcal,mol,1, depending on steric repulsion between substituents of the COT rings and protons of the central benzene ring. These DMTs form complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 1,2,4,5-tetracyano-benzene (TCNB) in solution and in the solid state. The binding abilities of these DMTs increase with electron-donating substituents on COT, which increase the electron densities of the cavity of the syn form, as supported by theoretical calculations. In addition, elongation of the terminal alkoxy chains of the DMTs was found to cause the enhancement of van,der Waals contact with guest molecules. Therefore, 5,b, which has CH2OMe groups on the COT rings and longer ethoxy groups on the terminal benzene rings, showed the highest electron density of the cavity and hence the highest binding ability with the electron-deficient guest molecules. Interestingly, solutions of 3,b, 4,b, and 5,b show thermochromism in the presence of DDQ. A solution of 3,b or 4,b with DDQ in CHCl3 is green due to charge-transfer interaction at room temperature and the color changes from green to yellow upon heating to 60,°C and from green to blue upon cooling to ,40,°C, whereas the high complexation ability of 5,b with DDQ only shows a change in the shade of blue. [source]


Systematic and morphological studies of the genus Chaetopleurophora Schmitz (Diptera: Phoridae) occurring in Japan

ENTOMOLOGICAL SCIENCE, Issue 4 2007
Hiroto NAKAYAMA
Abstract Japanese species of the genus Chaetopleurophora are reviewed. All belong to the C. erythronota group. The following three species from Japan are described: C. rhomboidea sp. nov., C. pygidialis Schmitz and C. dividua sp. nov. The male and female genitalia are studied and further examples of unique characters of the genus including asymmetric features are added. The male aedeagus of the genus is illustrated for the first time. The aedeagus of the species treated in this study consists of only two components, the inner core plate and the outer jacket plate. The jacket plate wraps sinistrally around the core plate. The combination of the core plate and the jacket plate forms complex, asymmetric features of the aedeagus in the Phoridae. The structure around the genital opening in the female genitalia protrudes posteriorly under the segment IX + X, and shows asymmetric features in C. rhomboidea sp. nov. with a bilaterally different degree of sclerotization, shifted genital opening to the right side and a membranous ribbon just on the left side. In addition, C. dividua sp. nov. is different from most of the species in the C. erythronota group, and very closely related to C. multiseriata (known in North America) in the male and female genitalia, wing venation and bristle formation on the scutellum. It is suggested that C. dividua sp. nov. forms a monophyletic group with C. multiseriata and the related species. [source]


Complexes of the Bicyclic Multifunctional Sulfur-Nitrogen Ligand F3CCN5S3 with Co2+, Zn2+, Cu2+, and Cd,

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2005
Carsten Knapp
Abstract The ability of the sulfur-nitrogen-carbon bicycle F3CCN5S3 to act as a donor towards transition metal cations has been investigated. F3CCN5S3 forms complexes with [M(SO2)2](AsF6)2 [M = Co, Cu, Zn, Cd] in the ratio 2:1 of the composition [M(F3CCN5S3)2(OSO)2(FAsF5)2] [M = Co (1), Zn (3)], [Cu(F3CCN5S3)2(,-F)(,-F2AsF4)]2 (4), and [Cd(F3CCN5S3)(,-F3CCN5S3)(,2 -F2AsF4)2]2 (5) in liquid sulfur dioxide. In the octahedral Co and Zn complexes F3CCN5S3 coordinates as a monodentate ligand through the bridging nitrogen atom N5, which carries the highest negative charge according to theoretical calculations. With Cu2+ a dinuclear structure with a central planar, four-membered Cu2F2 ring is formed, which has the shortest Cu···Cu distance of all structurally characterized Cu2F2 units. Similar to the Co and Zn complexes, F3CCN5S3 acts as a terminal monodentate ligand in the Cu compound. The reaction with the larger and softer Cd2+ cation results in a dinuclear complex that contains terminal and bridging F3CCN5S3 ligands. The bridging ligands coordinate through N5 and a nitrogen atom neighboring the carbon atom. In addition, a third weak bonding interaction between one fluorine atom of the trifluoromethyl substituent and the Cd2+ center is observed. The formation of the different structures and the versatile coordination modes of the F3CCN5S3 ligand are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]


GAK, a regulator of clathrin-mediated membrane trafficking, localizes not only in the cytoplasm but also in the nucleus

GENES TO CELLS, Issue 5 2009
Jun Sato
The ubiquitously expressed Cyclin G-associated kinase (GAK) regulates clathrin-mediated membrane trafficking in the cytoplasm. However, the association of GAK with a nuclear protein Cyclin G1 that is unrelated to membrane trafficking suggests an unidentified role of GAK in the nucleus. Indeed, we report here that GAK localizes in both cytoplasm and nucleus by immunostaining, ectopic expression of GFP-GAK and pull-down assays using dissected GAK fragments. GAK forms complexes not only with cyclin G1 but also with other nuclear proteins such as p53, clathrin heavy chain (CHC) and protein phosphatase 2A (PP2A) B,,1. Moreover, CHC associates with GAK via a different domain depending on whether it is in the cytoplasm or nucleus. Immunostaining revealed that about 20~30% of B,,1, cyclin G1 and p53 complex with nuclear GAK. CHC also displayed dots in the nucleus and almost all nuclear CHC signals colocalized with GAK. These observations together suggest an important function of GAK in the nucleus. [source]


Quantification of the expression level of integrin receptor ,v,3 in cell lines and MR imaging with antibody-coated iron oxide particles

MAGNETIC RESONANCE IN MEDICINE, Issue 4 2006
Sabrina Benedetto
Abstract Targeted imaging requires site-specific accumulation of a contrast agent (CA), and the properties of that agent must be selected according to the abundance of the target to obtain a signal above the detection limit of the instrument. However, numerical estimates of receptors per cell are rarely found in the literature. Integrin receptors would be particularly promising targets because of their accessibility from the blood stream and expression on activated neovascular endothelial cells. We systematically estimated the number of integrin receptors of cell lines and primary cells by flow cytometry analysis. Since integrin receptors are heterodimeric molecules, and ,v forms complexes with various , subunits, the numbers of ,v and ,3 subunits are therefore dissimilar. The observed values are 3 · 103,1.4 · 104/cell for ,v, and 5.3 · 102,1.1 · 104/cell for ,3. Despite the low number of exposed receptors, we show that up to single-cell MR visualization can be achieved with the use of iron oxide beads complexed with antibodies as CAs. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source]


Ligand Reprogramming in Dinuclear Helicate Complexes: A Consequence of Allosteric or Electrostatic Effects?

CHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2007

Abstract The ditopic ligand 6,6,-bis(4-methylthiazol-2-yl)-3,3,-([18]crown-6)-2,2,-bipyridine (L1) contains both a potentially tetradentate pyridyl-thiazole (py-tz) N - donor chain and an additional "external" crown ether binding site which spans the central 2,2,-bipyridine unit. In polar solvents (MeCN, MeNO2) this ligand forms complexes with ZnII, CdII, HgII and CuI ions via coordination of the N donors to the metal ion. Reaction with both HgII and CuI ions results in the self-assembly of dinuclear double-stranded helicate complexes. The ligands are partitioned by rotation about the central pypy bond, such that each can coordinate to both metals as a bis-bidentate donor ligand. With ZnII ions a single-stranded mononuclear species is formed in which one ligand coordinates the metal ion in a planar tetradentate fashion. Reaction with CdII ions gives rise to an equilibrium between both the dinuclear double-stranded helicate and the mononuclear species. These complexes can further coordinate s-block metal cations via the remote crown ether O - donor domains; a consequence of which are some remarkable changes in the binding modes of the N-donor domains. Reaction of the HgII - or CdII -containing helicate with either Ba2+ or Sr2+ ions effectively reprogrammes the ligand to form only the single-stranded heterobinuclear complexes [MM,(L1)]4+ (M=HgII, CdII; M,=Ba2+, Sr2+), where the transition and s-block cations reside in the N- and O-donor sites, respectively. In contrast, the same ions have only a minor structural impact on the ZnII species, which already exists as a single-stranded mononuclear complex. Similar reactions with the CdII system result in a shift in equilibrium towards the single-stranded species, the extent of which depends on the size and charge of the s-block cation in question. Reaction of the dicopper(I) double-stranded helicate with Ba2+ shows that the dinuclear structure still remains intact but the pitch length is significantly increased. [source]